1. Field of Invention
This invention relates to marine fenders. More particularly, this invention is directed to an improved marine fender having high energy absorbtion capacity and low reaction force and a shape and structure which eliminates expensive framework and external support material subject to snagging and frequent maintenance.
2. Description of the Prior Art
Marine fenders are used to absorb the impact energy between two ships, a ship and a quay or pier, a vessel and an off-shore oil platform, and other similar situations. Many types of fenders have been used for these various purposes, including bundles of rope and wood floats.
Currently most existing fender systems fall into one or more of three broad categories: (1) solid elastomeric shapes, (2) shock cells, and (3) low pressure fendering.
Solid elastomeric fenders include extruded or molded rubber shapes which will absorb a large amount of energy, but, because of the high compressive resistance of the elastomers, have small deflection and high reaction force. The high reaction force of this type fender generally limits its use to areas where vessel approach velocities are low or where vessels are small. Normally this type of fender is used with vessels, piers and docks in protected waters or for small boat landing on off-shore oil platforms.
Shock cell fenders usually incorporate solid elastomeric fenders on a metal frame with shock cells between the frame and the structure being fendered. The shock cells may be bodies of elastomeric material or may employ hydraulics, pneumatics, springs, etc. Shock cells generally absorb large amounts of enegy but also have high reaction forces. This type of fendering requires extensive metal framework and frequent maintenance, particularly in the case of pneumatic or hydraulic shock cells. Shock cell fenders are usually limited to use in fixed locations such as on off-shore oil platforms.
Low pressure fenders generally consist of an elastomeric skin filled with pressurized air or resilient foam. Usually these fenders operate at a contact pressure between 5 psi and 75 psi compared to several hundred psi for solid elastomeric and shock cell fenders. Low pressure fenders are usually contained within nets made of chain or wire rope and frequently incorporate used tires or rubber extensions as part of the net. The net is necessary to provide means for handling the fender or for transmitting loads from the fender to the rigging attaching the fender to the structure.
Low pressure fenders filled with air pressure require frequent monitoring of the inflation pressure and are subject to exploding or deflating if punctured. Both air and foam filled fenders require maintenance of the nets which are subject to snagging and wear. This type of fender is in widespread use in ship-to-ship and ship-to-dock applications, but is little used on off-shore oil platforms.
The fender of the invention combines many of the advantages of the three types of prior art fenders while eliminating their disadvantages. The unique design provides a fender having the high energy absorption capacity of solid elastomeric fenders and shock cell fenders and the low reaction force of the low pressure fenders. The fender design eliminates external nets common to low pressure fenders thus reducing maintenance and eliminating wear and snagging problems. The conical shape of the ends of the fender reduces the potential for snagging the fender on structure or vessel overhang, a common problem with cylindrical-shaped fenders.
While the fender of the invention has the high energy absorption capacity of solid elastomeric fenders, it is generally of larger diameter than the solid fenders thereby providing more stand-off distance between the vessel and the structure being fendered. In most instances this is advantageous, particularly with large vessels and in rough-sea situations such as for off-shore oil platforms.
Unlike shock cell fenders, the invention does not require an extensive steel framework and separate shock cells, thereby reducing the cost of the fendering system and the maintenance required. Furthermore, although providing energy absorption comparable to a shock cell fender, the invention is more versatile in use since it does not have the extensive structural framework; it may be easily relocated or removed and replaced.